Efficient triplet harvesting by fluorescent molecules through exciplexes for high efficiency organic light-emitting diodes

Efficient triplet harvesting from exciplexes by reverse intersystem crossing (RISC) is reported using a fluorescent molecular system composed of the 4,4′,4″-tris(N-carbazolyl)-triphenylamine and bis-4,6-(3,5-di-3-pyridylphenyl)-2-methylpyrimidine. The exciplex forming material system shows the efficient delayed fluorescence emission. As a result, almost 100% PL efficiency at 35 K and 10% external quantum efficiency at 195 K are achieved from the exciplex. The delayed fluorescence of the exciplex clearly demonstrates that a significant proportion of the triplet exciplexes is harvested through the RISC.